Re: [PATCH] ovl: use linked upper dentry in copy-up tmpfile

[Amir Goldstein]

On Sat, May 2, 2026 at 1:27 AM Souvik Banerjee <souvik@xxxxxxxxxxxx> wrote:
>
> ovl_copy_up_tmpfile() stores the disconnected O_TMPFILE dentry as the
> overlay's upper dentry reference via ovl_inode_update().  vfs_tmpfile()
> allocated this dentry via d_alloc(parentpath->dentry, &slash_name), so
> d_name is "/" and d_parent is c->workdir.  Local upper filesystems
> (ext4, btrfs, xfs, ...) immediately rename it to "#<inum>" via
> d_mark_tmpfile() inside their ->tmpfile() op; FUSE and virtiofs do
> not, so both fields stay that way.  Neither identifies the destination
> directory and filename where ovl_do_link() actually linked the file.
>
> When the upper filesystem implements ->d_revalidate() (e.g. FUSE or
> virtiofs), ovl_revalidate_real() calls it with the dentry's parent
> inode and a snapshot of d_name.  The server tries to look up "/" inside
> c->workdir, fails, and overlayfs reports -ESTALE.
>
> This causes persistent ESTALE errors for any file that was copied up via
> the tmpfile path, breaking dpkg, apt, and other tools that do
> rename-over-existing on overlayfs with a FUSE/virtiofs upper.
>
> Before commit 6b52243f633e ("ovl: fold copy-up helpers into callers"),
> the tmpfile copy-up path used a dedicated helper ovl_link_tmpfile()
> that captured the linked destination dentry returned by ovl_do_link():
>
>     err = ovl_do_link(temp, udir, upper);
>     ...
>     if (!err)
>         *newdentry = dget(upper);
>
> and published it via ovl_inode_update(d_inode(c->dentry), newdentry).
> The fold inlined ovl_do_link() into ovl_copy_up_tmpfile() but dropped
> the dget(upper) capture, and rewrote the publish line as
> ovl_inode_update(d_inode(c->dentry), dget(temp)) — where temp is the
> disconnected O_TMPFILE dentry.
>
> Fix by keeping a reference to the linked destination dentry after
> ovl_do_link() succeeds, and publishing that dentry at the existing
> ovl_inode_update() call site.  The non-tmpfile/workdir path continues to
> publish the renamed temporary dentry.
>
> Reproducer:
>   - Mount overlayfs with virtiofs (or a FUSE fs whose server advertises
>     FUSE_TMPFILE) as upper
>   - Run: dpkg -i <any .deb>
>   - Observe: "error installing new file '...': Stale file handle"
>
> Fixes: 6b52243f633e ("ovl: fold copy-up helpers into callers")
> Cc: stable@xxxxxxxxxxxxxxx # v4.20+
> Signed-off-by: Souvik Banerjee <souvik@xxxxxxxxxxxx>
> ---
>  fs/overlayfs/copy_up.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 13cb60b52bd6..e963701b4c87 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -853,7 +853,7 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
>  {
>         struct ovl_fs *ofs = OVL_FS(c->dentry->d_sb);
>         struct inode *udir = d_inode(c->destdir);
> -       struct dentry *temp, *upper;
> +       struct dentry *temp, *upper, *newdentry = NULL;
>         struct file *tmpfile;
>         int err;
>
> @@ -889,6 +889,14 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
>         err = PTR_ERR(upper);
>         if (!IS_ERR(upper)) {
>                 err = ovl_do_link(ofs, temp, udir, upper);
> +               if (!err) {
> +                       /*
> +                        * Record the linked dentry -- not the disconnected
> +                        * O_TMPFILE dentry -- so that ->d_revalidate() on
> +                        * the upper fs sees the real parent/name.
> +                        */
> +                       newdentry = dget(upper);
> +               }
>                 end_creating(upper);
>         }
>
> @@ -903,7 +911,7 @@ static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
>
>         if (!c->metacopy)
>                 ovl_set_upperdata(d_inode(c->dentry));
> -       ovl_inode_update(d_inode(c->dentry), dget(temp));
> +       ovl_inode_update(d_inode(c->dentry), newdentry);
>
>  out:
>         ovl_end_write(c->dentry);
> --
> 2.51.1
>


Hi Souvik,

Thank you for the analysis and the fix.
Looks correct to me.

Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>

Christian,

Could you pick this up for vfs-fixes?
I do not have any other ovl fixes queued up.

Thanks,
Amir.